Current administration policy is replete with examples of quickly enacted efforts whose consequences led to the opposite effect. (Beware of what you wish for . . . .) With Congress caving last week, the National Security Agency no longer needs a Foreign Intelligence Surveillance Act warrant to wiretap if one party is believed to be outside the United States. This change looks reasonable at first, but it could create huge long-term security risks for the United States.

The immediate problem is fiber optics. Until recently, telecommunication signals came through the air. The NSA used satellites and antennas to pick up conversations of foreigners talking to other foreigners. Modern communications, however, use fiber; since conversations don't go through the air, the NSA wants to access communications at land-based switches.

Because communications from around the world often go through the United States, the government can still get access to much of the information it seeks. But wiretapping within the United States has required a FISA search warrant, and the NSA apparently found using FISA too time-consuming, even though emergency access was permitted as long as a warrant was applied for and granted within 72 hours of surveillance.

Avoiding warrants for these cases sounds simple, though potentially invasive of Americans' civil liberties. Most calls outside the country involve foreigners talking to foreigners. Most communications within the country are constitutionally protected – U.S. “persons” talking to U.S. “persons.” To avoid wiretapping every communication, NSA will need to build massive automatic surveillance capabilities into telephone switches. Here things get tricky: Once such infrastructure is in place, others could use it to intercept communications.

Grant the NSA what it wants, and within 10 years the United States will be vulnerable to attacks from hackers across the globe, as well as the militaries of China, Russia and other nations.

Such threats are not theoretical. For almost a year beginning in April 2004, more than 100 phones belonging to members of the Greek government, including the prime minister and ministers of defense, foreign affairs, justice and public order, were spied on with wiretapping software that was misused. Exactly who placed the software and who did the listening remain unknown. But they were able to use software that was supposed to be used only with legal permission.

The United States itself has been attacked. In six hours in August 2006, remote attackers entered computers at the Army Information Systems Engineering Command at Fort Huachuca, Ariz.; the Defense Information Systems Agency in Arlington, Va.; the Naval Ocean Systems Center in San Diego; and the Army Space and Strategic Defense Command in Huntsville, Ala. The hackers transported more than 10 terabytes of data to South Korea, Hong Kong or Taiwan, and from there to the People's Republic of China. Each intrusion was only 10 to 30 minutes. The downloaded information included Army helicopter mission-planning-systems specifications and flight-planning software used by the Army and Air Force.

U.S. communications technology is fragile and easily penetrated. While advanced, it is not decades ahead of that of our friends or our rivals. Compounding the issue is a key facet of modern systems design: Intercept capabilities are likely to be managed remotely, and vulnerabilities are as likely to be global as local. In simplifying wiretapping for U.S. intelligence, we provide a target for foreign intelligence agencies and possibly rogue hackers. Break into one service, and you get broad access to U.S. communications.

The Greek wiretapping and Chinese thefts from U.S. military sites are warnings that entities other than the NSA could exploit the vulnerabilities of U.S. communications networks. Were the proposed wiretapping technology penetrated by foreign intelligence services, U.S. security and privacy could be quickly and severely compromised.

To provide policy-makers with immediate intelligence, the NSA forgot the critical information security aspect of its mission: protecting U.S. communications against foreign interception. So did Congress. Lawmakers granted the warrantless wiretapping only for six months – and they need to look carefully before it endangers U.S. national security for the long term.

Landau, co-author of “Privacy on the Line: The Politics of Wiretapping and Encryption,” is an engineer at Sun Microsystems Laboratories.